The present invention relates to a brake device of a motor having a speed reducing mechanism used in a power window device that selectively opens and closes a window glass of, for example, an automobile, and to a motor having a speed reducing mechanism having the brake device.
As a conventional brake device, a brake device described in Japanese Laid-Open Patent Publication No. 2002-130336, for example, is known. The brake device includes a first rotor rotatable integrally with a drive shaft and a second rotor rotatable integrally with a driven shaft, which is arranged coaxially with the drive shaft. The brake device includes a braking mechanism and a cam mechanism. The braking mechanism has a movable friction member rotatable integrally with the second rotor, an urging member arranged between the movable friction member and the second rotor, and a fixed friction portion. The braking mechanism is capable of moving the movable friction member between an engagement position and a non-engagement position while rotating the movable friction member in the same direction as the rotational direction of the drive shaft. When located at the engagement position, the movable friction member contacts the fixed friction portion due to urging force produced by the urging member. When located at the non-engagement position, the movable friction member is spaced from the fixed friction portion against the urging force of the urging member. The cam mechanism moves the movable friction member between the engagement position and the non-engagement position. When rotational force is applied from the drive shaft to the first rotor, the cam mechanism receives the rotational force from the first rotor and switches the position of the movable friction member from the engagement position to the non-engagement position. The rotational force of the first rotor is transmitted to the second rotor through the cam mechanism. In contrast, if rotational force is applied from the driven shaft to the cam mechanism, the cam mechanism restricts rotation of the driven shaft by maintaining the movable friction member at the engagement position.
However, in the above-described brake device, the cam mechanism receives all the rotational force of the first rotor when the rotational force is provided from the drive shaft. It is thus necessary to ensure such strength of the cam mechanism that the cam mechanism tolerates the rotational force. This enlarges the size of the cam mechanism and increases the cost, for example.